We went with a split age group (at the time, me-45, DD -16, DS -13, DN - 12, DN -9, DN 3.5, my mom - 70, sister - 42 and BIL - 50). We found what worked best for us was to plan a period of time to do the rides that everyone could do together. Other times the thrill riders went off and did the bigger rides while the non-thrill riders did the tamer stuff. The adults switched off with the youngest so everyone had a chance to ride/see what they wanted to at least once while we were there.
Unless you're staying on-site some of the lines for the bigger rides can get really long (it can even be a bit of a wait with on-site). We tried having the bigger kids go on the thrill rides and waiting for them and found the younger children got really bored and out of sorts waiting for the older ones.